The present invention relates generally to the field of switch mode power supply (SMPS). More particularly, embodiments of the present invention relate to SMPS with a buck converter circuit for providing a constant output current.
Switch mode power supply (SMPS) systems have many advantages over convention linear regulated power supplies. These advantages include smaller volume, better stability, and higher power efficiency. As a result, SMPS has found wide spread applications, such as televisions, set-top boxes, video recorders, portable telephone chargers, and personal digital assistants (PDAs), etc. In recently years, as light emitting diode (LED) technologies are becoming more mature, SMPS is widely used as drivers for LED devices, including back lighting for display devices and white-light bulb replacement applications.
Switched mode power supply systems can be isolated or non-isolated. In isolated power supplies, a transformer is used to transfer energy between the primary side and the secondary side. In a non-isolated switched mode power supply system, a power switch is connected to an inductor, which is also connected to the output. Magnetic energy is stored in the inductor when the switch is turned on, and the energy is transferred to the output when the switch is turned off. A buck converter, also known as a step-down converter, is an example of non-isolated switched mode power supply system that has been used in driving LED lighting systems because of its simple circuit topology and low cost.